Ceramic substrates for electronic applications are becoming more dense with the evolution of new technology. However, increases in circuit density produce a corresponding increase in overall manufacturing problems. Ceramic substrates manufacturers are therefore constantly challenged to improve the quality of their products by identifying and eliminating problems which produce defective parts. Whereas significant improvements are being made to eliminate systematic defects by reducing process variability. Process improvements alone are not sufficient to eliminate all the random defects which effect both yield and reliability. Historically, screening techniques have been employed to improve product failure rates to acceptable levels by culling out many of these random defects.
Normally, these ceramic substrates are made by using casting slurry or ceramic slip of material contained in a hopper. The slip material is typically a mixture of ceramic powder, organic binder and solvents. The ceramic tape or the green sheet is formed with the extrusion of a film of slurry on to a supporting or carrier strip or sheet, using a method known in the art as doctor blading. The ceramic slurry which is on the upper surface of the supporting strip is processed through a conventional belt type oven and the cured ceramic sheet along with the backing or carrier material is then spooled onto a spool. The conventional method of slitting the ceramic sheet is to cut through the cured ceramic tape forming individual blanks or green sheets. This conventional cutting process produces ceramic debris because this cutting is done to the solid cured ceramic sheet, which also creates contamination. The debris from the ceramic also creates other problems, such as, for example, defective parts, cleaning of the equipment, etc., and this of course adds cost to the process.
U.S. Pat. No. 1,998,357 (Carlson) discloses a web cutting and scoring device. A web of sheet material is brought in contact with a plurality of cutter knives and rotary scoring blades to create tracks, in order to either cut or score the web of sheet material into strips. A backing roller also helps provide the necessary pressure in the scoring or cutting operation of the web of sheet material.
U.S. Pat. No. 4,570,518 (Burmeister) discloses an apparatus for slitting of continuous webs into ribbons. The web material passes between a plurality of cutting blades and a backing roller and are cut into individual ribbons.
U.S. Pat. No. 5,051,219 (Miller) discloses an automatic handling of green ceramic tapes. A green ceramic tape on a supporting strip is rolled off a flanged roller. The supporting strip is then separated from the green ceramic tape and is wound-up on a spool for possible reuse, while the green ceramic tape is processed through a blanking press to form a plurality of blanking cards.
The above-mentioned problems of the prior art have been solved by the method and apparatus of this invention where the green sheet is unconventionally indented during the initial stages of the curing process and the curing process automatically divides the indented ceramic sheet into tapes or ribbons during the curing stage and these tapes or ribbons are free of any cutting contamination.